I like to think that she was a failed attempt of cloning Peach. (Sort of like Wario.) Now she is very mischievous and always keeps a trick up her sleeve. Buuuuut- She always hides it by acting overly joyful. Poor Bowser.
My little brother also suggested that maybe she was made by Rosalina so she would feel closer to her mother...
Or maybe Nintendo was lazy and high and were like: ''Hey. Metal Mario looks pretty in HD. Let's make a re-skin of Peach!
Green Bronze Luigi confirmed.
#PinkGoldPeach